Borescope inspection ports are currently in common use on most gas turbine engines. Borescope ports allow visual inspection of internal aircraft engine flowpath hardware with a fiber optic borescope. These borescope ports thereby make possible frequent critical engine inspections that otherwise could not be performed without disassembly of the aircraft engine. This allows increased engine usage between overhaul and thus lowers aircraft engine operating costs.
During engine operation borescope plugs are used to close the inspection ports on the engine and prevent the escape of high pressure engine gases. Conventional borescope plugs typically resemble the prior art borescope plug 10 shown in FIG. 1. The plug 10 closes a port 12 through an inner casing 14 and seals the flowpath structure 16 at port 18. A spring loaded plunger 20 seals against the port 18. A conventional bolt head 22 is provided for assembling and disassembling the plug from the threaded mount 24. The engines outer flowpath 26 is sealed with a cover plate 28.
There are several deficiencies with conventional borescope plugs having designs similar to that shown in FIG. 1. A major problem is that these plugs are difficult to assemble to and disassemble from the engine's inner case. Disassembly requires removal of the cover plate 28 and the snaking of a tool through the hole in the outer casing 26 and onto the borescope plug at bolt head 22. When the borescope plug is unscrewed from the mount 24, it is slowly removed with the tool. If the plug falls off the tool it can fall freely in the space between the inner and outer ducts. This would require duct removal for plug recovery. Assembly of the conventional plug to the engine comprises the reverse of the above steps. Thus assembly and disassembly of this conventional style plug takes a certain degree of skill and luck to avoid accidental misplacement of the plug.
Another deficiency with conventional borescope plugs is the uncertainty of whether or not the borescope plug is in place during engine inspection. If cover plate 28 is inadvertently resecured over removal hole 30 while the borescope plug is out of position visual inspection will not ascertain the problem. Open borescope holes through the flowpath and inner duct will result in poor engine operation.
A further undesireable characteristic of the conventional borescope plug is that the plug tip 32 does not conform to the flowpath surface. This can result in airflow problems and, in certain areas of the engine, in overheating of the tip 32 due to stagnating heated air. This is particularly a problem in areas with an angled or conical flowpath.
A need therefore exists for an improved borescope plug that is easy to assemble and disassemble from a turbine engine.
A further need exists for a borescope plug that is easy to visually inspect prior to engine operation.
A need also exists for an improved borescope plug that has minimal impact on engine airflow and is suitable for use in high temperature flowpath areas.